Anodic polarographic waves corresponding to the formation of mercury compounds at the surface of the dropping mercury electrode provide a convenient method for the determination of inorganic anions such as sulphide and the halides 1, 2, and many organosulphur compounds (e.9. dithiocarbamates). Because of the use of dithiocarbamates in pesticides and fungicides their determination by polarographie and related techniques has recently received considerable attention 3-6.
Useful analytical data for these anodic electrode processes is often difficult to obtain because of the formation of films of insoluble reaction product on the electrode surface. Rapid direct current (d.c.) polarography has been shown to be effective in eliminating the abnormal behaviour associated with these films 7. However, the sensitivity of d.c. polarography, limited by the double-layer charging current, is sometimes insufficient for trace analysis and it may be necessary to consider other techniques for such work.
Pulse polarography is one of the techniques that has been developed to discriminate against the charging current. The differential pulse mode, in which a pulse of fixed amplitude is superimposed on a linearly increasing d.c. voltage, has the convenient peak form of readout. Although this method has been shown to be particularly suitable for trace analysis, because of improved sensitivity compared with d.c. polarography, its analytical applications have not been fully exploited. Evaluation of the technique has usually been carried out with electrode processes involving reversible reduction 0 fcations 8, although some irreversible reduction processes have also been studied 9.
This paper investigates the applicability of differential pulse polarography to the important class of electrode processes involving oxidation of mercury accompanied by formation of an insoluble mercury compound. As well as comparing the sensitivity of this technique with d.c. polarography, the effect of pulse amplitude on analytically important parameters such as peak height and peak half-width have been investigated and compared with an earlier theoretical and experimental evaluation s .
The species studied were chloride, bromide, iodide, sulphide and sodium diethyldithiocarbamate (NaDtc).